on Serbia and the advance of the Bulgaria First and Second armies during the subsequent Serbian Campaign. Romania's neutrality during this period allowed the Bulgarian high command to use the Third Army as a reserve force for the operations in Macedonia and in the middle of 5 October, Danube Division was ordered to join the Second Army's operations against the Serbians and the Allied advance from Salonika. To compensate for this loss the command used the garrisons of Oryahovo, Gigen, Somovit, Nikopol and Svishtov as well as 2 March Brigade to form a new 12th Mixed Infantry Division. On 14 October a Russian fleet that included the battleships Imperatritsa Mariya, Evstafi, Ioann Zlatoust, Panteleimon, the cruisers Pamiat Merkuria and Kagul supported by eighteen smaller vessels bombarded the port of Varna. The force fired several hundred shells but came under the attack of German submarines 17 and 18 and retired by noon of the same day. The damage on the shore was light and only a few soldiers and some 27 civilians became casualties. After the attack the Army command took measures against a possible Russian landing in the vicinity of Varna – the coastal artillery was strengthened, new mines were laid in the sea and the Bulgarian high command made steps to acquire the navy's first submarine from the Germans that officially entered service in May 1916. Bulgarian morale was also raised by the arrival of the German 105th Infantry Division during November and in February 1916 the Bulgarian high command ordered the entire 1st Sofia Infantry Division to be transferred from Macedonia to Northern Bulgaria, where it arrived a month later. The 11,287 men of the 105th Division formed the mobile forces of the army in the coastal areas and were ordered by General Toshev to defend the coast and repel any amphibious landings in the area of Varna and Burgas. For the next several months no such landing materialized and in May 1916 the Bulgarian and German high commands agreed to send the 105th Division to Macedonia with the exception of a single infantry battalion, two machine guns and the 105th heavy battery that were to remain in Shumen and Varna. Nevertheless, rumors that a Russian army was concentrating in the Crimea for a sea invasion of the Bulgarian coast in conjunction with an allied offensive in Macedonia continued to arrive in the Bulgarian high command headquarters. This